我正在尝试使用来自此链接的基本 Camera2 在 camera2 预览上绘制一个矩形: https://github.com/googlesamples/android-Camera2Basic

我在论坛上关注了这个问题的答案:

android Camera2 API + TextureView overlay for drawing on camera preview

但我无法让它工作。如果您能帮我弄清楚如何解决我的问题，我将不胜感激。这是用于绘制矩形的类:Rectangle.java

package com.example.android.camera2basic;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.view.View;

public class Rectangle extends View {
Paint paint = new Paint();

public Rectangle(Context context) {
    super(context);
}


@Override
public void onDraw(Canvas canvas) {
    paint.setColor(Color.GREEN);
    paint.setStyle(Paint.Style.FILL);
    Rect rect = new Rect(20, 56, 200, 112);
    canvas.drawRect(rect, paint );
}
}

相机的xml文件activity_camera.xml:

<?xml version="1.0" encoding="utf-8"?>

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#000"
tools:context="com.example.android.camera2basic.CameraActivity">

<LinearLayout
android:id="@+id/surface"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" />

</FrameLayout>

这是在我将矩形添加到相机预览 Camera2BasicFragment.java 的类中使用的方法:

  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    View view = inflater.inflate(R.layout.fragment_camera2_basic, container, 
    false);
    LinearLayout linearLayout = (LinearLayout) 
    view.findViewById(R.id.surface);
    linearLayout.addView(new Rectangle(getActivity()));
    return view;
    }

最后在应用程序启动时崩溃后出现错误:

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.camera2basic/com.example.android.camera2basic.CameraActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.LinearLayout.addView(android.view.View)' on a null object reference
                                                                                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2793)
                                                                                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2864)
                                                                                  at android.app.ActivityThread.-wrap12(ActivityThread.java)
                                                                                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1567)
                                                                                  at android.os.Handler.dispatchMessage(Handler.java:105)
                                                                                  at android.os.Looper.loop(Looper.java:156)
                                                                                  at android.app.ActivityThread.main(ActivityThread.java:6523)
                                                                                  at java.lang.reflect.Method.invoke(Native Method)
                                                                                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:941)
                                                                                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:831)
                                                                               Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.LinearLayout.addView(android.view.View)' on a null object reference
                                                                                  at com.example.android.camera2basic.Camera2BasicFragment.onCreateView(Camera2BasicFragment.java:431)
                                                                                  at android.app.Fragment.performCreateView(Fragment.java:2361)
                                                                                  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1000)
                                                                                  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1178)
                                                                                  at android.app.BackStackRecord.run(BackStackRecord.java:815)
                                                                                  at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1585)
                                                                                  at android.app.FragmentController.execPendingActions(FragmentController.java:371)
                                                                                  at android.app.Activity.performStart(Activity.java:6929)
                                                                                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2756)
                                                                                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2864) 
                                                                                  at android.app.ActivityThread.-wrap12(ActivityThread.java) 
                                                                                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1567) 
                                                                                  at android.os.Handler.dispatchMessage(Handler.java:105) 
                                                                                  at android.os.Looper.loop(Looper.java:156) 
                                                                                  at android.app.ActivityThread.main(ActivityThread.java:6523) 
                                                                                  at java.lang.reflect.Method.invoke(Native Method) 

最佳答案

感谢@cricket_007 的评论，我发现了我的错误。我在错误的 xml 文件中初始化 LinearLayout。它应该在 fragment_camera2_basic.xml

此外，要设法在相机预览上获得矩形，您应该在这段代码之后添加它:

<com.example.android.camera2basic.AutoFitTextureView
    android:id="@+id/texture"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentStart="true"
    android:layout_alignParentTop="true" />

所以最终的 xml 文件看起来像这样 fragment_camera2_basic.xml :

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">


    <com.example.android.camera2basic.AutoFitTextureView
        android:id="@+id/texture"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true" />
    <LinearLayout
        android:id="@+id/surface"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical" />

    <FrameLayout
        android:id="@+id/control"
        android:layout_width="match_parent"
        android:layout_height="112dp"
        android:layout_alignParentBottom="true"
        android:layout_alignParentStart="true"
        android:background="@color/control_background">

        <Button
            android:id="@+id/picture"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:text="@string/picture" />

        <ImageButton
            android:id="@+id/info"
            android:contentDescription="@string/description_info"
            style="@android:style/Widget.Material.Light.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_vertical|right"
            android:padding="20dp"
            android:src="@drawable/ic_action_info" />

    </FrameLayout>

</RelativeLayout>

P.S:要设法使矩形未填充，请在 Rectangle.class 中使用它:paint.setStyle(Paint.Style.STROKE);

关于android - 在 camera2 预览 android 上绘制矩形，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/44749473/